Proximity sensors have many different applications in many different industries. In the aerospace industry, for example, proximity sensors can be used within an aircraft to detect the position of various movable components. For example, proximity sensors can be used to detect the position of aircraft landing gear, landing gear doors, spoilers, passenger doors, and/or cargo doors. In this regard, such proximity sensors can be used to indicate aircraft conditions such as weight-on-wheels, landing gear up/down, doors open/closed, and/or spoilers stowed/not stowed.
As will be appreciated, proximity sensors can be configured to detect the presence of an object in accordance with a number of different techniques including, for example, variable reluctance, eddy current loss, saturated core, and the Hall effect. Inductive proximity sensors typically include a core of a highly-permeable metal, where the core includes at least one, and more typically two, legs. Inductive coils are wound around one or more bobbins, which are placed over each leg of the core and bonded to the core, such as by means of an epoxy. While the shape of the core can vary, in one typical configuration, the core can comprise a C-shaped core. In such an instance, two coils are typically wound around bobbin(s), and placed over the legs of the core, in opposite directions (one wound clockwise and the other wound counter-clockwise) and electrically connected in series.
In accordance with a variable-reluctance proximity detection technique, an external AC current source drives the coils of the proximity sensor such that the proximity sensor generates an alternating magnetic field. Then, when a permeable and/or conductive object is brought or otherwise moved into the alternating magnetic field, the reluctance (i.e., air gap resistance) between the object and the proximity sensor changes, or more particularly, decreases. As the reluctance decreases, the inductance of the coils increases. This increase can then be measured to thereby detect the proximity of the object.
As indicated, the inductive coils of a proximity sensor are conventionally wound around bobbins, which are placed over and bonded to each leg of the core of the proximity sensor. In many conventional proximity sensors, these bonds can be undesirably weak, thereby increasing the likelihood of sensor failure, particularly under high-shock conditions. In addition, as bonding epoxies typically exhibit a high coefficient of thermal expansion, the bobbins and inductive coils wound around the bobbins, may move relative to the core during operation under higher-temperature conditions. Movement of the bobbin relative to the core may result in a change in the measured inductance of the sensor, which in various instances can exceed required sensor tolerances.